Issue 3623: _json: fix raise_errmsg(), py_encode_basestring_ascii() and linecol()

_json module of python 3.0 has some bugs.

(a) [_json.c] raise_errmsg() calls json.decoder.errmsg() from Python 
module, but this function may fails. If it fails, error should be be 
set to NULL. Example:

>>> import _json
>>> _json.scanstring(b"xxx", 1, "xxx")
Erreur de segmentation (core dumped)

=> json.decoder.errmsg() calls linecol() which raise an error on 
b"xxx".index("\n").

(b) [_json.c] py_encode_basestring_ascii() calls PyBytes_Check(rval) 
but rval can be NULL if ascii_escape_str() or ascii_escape_unicode() 
fails. Example:

>>> import _json
>>> _json.encode_basestring_ascii(b"xx\xff")
Erreur de segmentation (core dumped)

(c) [Lib/json/decoder.py] linecol() doesn't support bytes, but it's 
called with bytes argument: see point (a). For an example, see point 
(a).

That patch looks ok to me, but I'm not at all familiar with the changes in 
python 3.0 yet. Is this something that needs to be backported to 2.6?

Christian, I believe, did the original 3.0 porting, so he can probably
shed some light on this.

Deferring until rc2

issue3763 mentions about the similar problem with json library.
The traceback posted illustrates the issue (c) mentioned here:

  File "C:\Python30\lib\json\decoder.py", line 30, in errmsg
    lineno, colno = linecol(doc, pos)
  File "C:\Python30\lib\json\decoder.py", line 21, in linecol
    lineno = doc.count('\n', 0, pos) + 1
TypeError: expected an object with the buffer interface

> Is this something that needs to be backported to 2.6?

Hum, here is a part of my patch which can be applied to python 2.6. I 
don't know if it fixes real bugs, but the code looks better with the 
patch: PyErr_SetObject() and Py_DECREF() should not be called with 
NULL argument.

_json26.patch looks good, and is necessary, because the called python
function has more than one way to raise an exception (KeyboardInterrupt
at least...)

I would just add another minor change: this raise_errmsg() function
should be made static.

I applied the changes proposed in _json26.patch to simplejson and they 
worked perfectly fine. Again I'm not the best judge of python 3.0 code 
because I have not made myself familiar with the API changes so someone 
else should review it (but it's probably fine).

The patch looks good to me. 

You may want to fix the refleak in the PyList_Append() calls (I counted
4) too:

            if (PyList_Append(chunks, chunk)) {
                goto bail;
            }

should be:

            if (PyList_Append(chunks, chunk)) {
                Py_DECREF(chunk);
                goto bail;
            }

Also, line 384 and 548:

    Py_DECREF(chunks);
    chunks = NULL;

should changed to

    Py_CLEAR(chunks);

Fixed in r66932 and r66934.

Refleak was fixed in r66934.

I mean r66938. Sorry!